Method and system for maintaining an electrically neutral atmosphere

ABSTRACT

A method and system for maintaining precise electrically neutral, positive or negative atmosphere in an area, such as a textile mill, by adding charged ions to air being pumped into that area, for example through an air conditioning duct whereby at least two spaced apart grids are mounted in the duct with one connected to a positive high voltage source and the other connected to a negative high voltage source so that both grids produce ions and the voltages applied thereto are controlled to maintain the area atmosphere neutral, positively charged or negatively charged as required to dissipate an undesired charge generated in a manufacturing process.

BRIEF DESCRIPTION OF THE PRIOR ART AND SUMMARY OF THE INVENTION

The invention relates to a method and system for maintaining anelectrically neutral or positively or negatively charged atmosphere in agiven area such as a textile mill.

Almost any area, particularly a confined area where large machines arein operation, such as a textile mill, has either a positive or negativeelectrical field. In most instances, this field is undetectable andcauses no problem with respect to the desired activities that are beingundertaken in the area. However, in certain situations, particularly inconjunction with operation of textile machines, such as looms or thelike, even a rather small electrical field causes problems with regardto proper operation of the machines. One such problem is the undesirablebuildup or accumulation of lint on machine parts. Accordingly, it isusually desirable to attempt to maintain an atmosphere in the area whichis as close to electrically neutral as possible, or biased with apolarity opposite to the charge generated by the manufacturing process.

In the past, there has been a number of attempts to automatically adjustthe electrical field within an area by supplying ions of a polarityopposite to that of a detected field until an essentially neutral fieldcondition has been produced. For example, the patent to Michener et al.,U.S. Pat. No. 3,387,181, describes a system in which ions passingthrough a tube are collected on metallic wire pads and counted. A directcurrent charged grid disposed in the main air stream of an aircirculating system is then controlled in polarity and intensity of gridcurrent as a function of the detected ion count so as to maintain aneutral atmosphere in the room. This type of device has severaldrawbacks which make it impractical for most applications.

First, the grid current is not regulated directly as a function of theelectrical field within the work area but rather as a function of theions which are counted in a tube. This count is, therefore, onlygenerally related to the field potential within the room. It is possiblethat a considerable electrical field may exist without the existence ofeven a small number of ions. Further, the Michener reference is slow inresponding to changes in electrical field potential within the area andtends to overshoot when correcting a positive or negative potential.

The U.S. Pat. to Huber, No. 3,870,933, Ser. No. 384,229 filed July 31,1973, describes another system of this type which, however, employs aunique detector element which produces an ion cloud in the vicinity of ametallic probe. The ion cloud interacts with the electrical field in thearea that is desired to be kept electrically neutral to produce a signalindicating the polarity and magnitude of the electrical field. Thiscontrol signal can then be used to control arrangements for addingpositive and negative ions to the air conditioning system, for example,by the use of chemicals or the like. The patent further mentions that agrid can be placed in the air conditioning duct to emit ions toneutralize the electrical field in response to the signal provided bythe unique detector.

Most textile areas are electrically negative so that positive ions mustbe added to the room to bring it back to an electrically neutralcondition or a predetermined positive level. However, occasionallypositive electrical fields are produced and it is desirable also in anysystem to have the ability to produce negative ions and thus bring apositive electrical field back to a less positive, neutral condition, orperhaps a negative condition. When using an electrical grid to which ahigh voltage is applied to generate ions, one of two techniques can beemployed to give the system flexibility to produce either negative orpositive ions.

First, a single grid can be mounted in the duct and a switch providedfor coupling the grid either to a negative or a positive power supply.However, in view of the high voltages which are normally applied to thegrids, switching of the grid from one power source to the other isdifficult and undesirable. The alternative technique is to provide twogrids which are spaced apart, one of the grids connected to a positivepower source and the other grid connected to a negative power sourcewith care taken in the prior art not to allow the two power supplies tooperate at the same time.

According to the invention of this application, it has been discoveredthat providing two spaced apart grids in an air conditioning duct or thelike, which supplies air to a room to be kept electrically neutral or ata precise positive or negative level and operating both at the same timeto produce both positive and negative ions surprisingly requires lesspotential on the grid contacted last by the air flowing within the ductfor maintaining a given desired atmospheric charge level than a singlepositive grid in a situation where positive ions must be added toneutralize a negative electrical field. Further, overshoot problems aredramatically reduced and in many instances are substantially eliminatedwhen correcting such a field by the invention of this application. Ithas been found that a grid comprised of a number of individual finewires extending roughly in parallel with a spacing of, for example threeinches, provides satisfactory operation and it has further been foundthat a separation between the positive and negative grids of between 6and 18 inches, and preferably 12 inches, produces desirable results.

While the reasons for these surprising results are not entirelyunderstood, it is believed that the interaction of each grid with theions of the opposite polarity and the resultant acceleration ordeceleration of these ions as a result of that interaction plays somepart in the results. It is further believed that by adjustment of thegrid connected to the polarity which is the same as the polarity of theelectrical field to be neutralized, overshoot in the neutralizingprocess is reduced.

Many other objects and purposes of the invention will be clear from thefollowing detailed description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic side view of the unique grids of thisinvention, mounted in an air conditioning duct which supplies air to aroom or the like which is to be kept in electrically neutral or anydesired positive or negative condition;

FIG. 2 shows a perspective view of one of the grids of this inventionmounted in an air conditioning duct;

FIG. 3 shows a view of the upper grid connection;

FIG. 4 shows an electrical schematic of the unique circuitry of thisinvention for applying appropriate voltages to the two grids to causethe air in the room where the sensor is located to be kept in anelectrically neutral or any desired positive or negative condition.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is now made particularly to FIGS. 1-3 which illustrate theunique construction of the grid of this invention. Grids 20 and 22 arepreferably mounted as shown in an air conditioning duct which leadsdirectly into the room that is to be maintained in an electricallyneutral condition. It has been found that results are optimized for aplant which is generally negative, and to which accordingly must besupplied positive ions, by mounting the grid to which is coupled thenegative power supply so that air flows first through the negative gridbefore encountering the grid to which the positive power supply isconnected. In the arrangement of FIG. 1, the grid 20 accordingly wouldpreferably be connected to a negative power supply while the grid 22would preferably be connected to a positive power supply.

Further, it has been found that results are optimized for a plant whichis generally positive, and to which accordingly must be suppliednegative ions, by mounting the grid to which the positive power supplyis coupled so that air flows first through the positive grid beforeencountering the grid to which the negative power supply is connected.In this arrangement, the grid 20 in FIG. 1 would become the positivegrid and would, therefore, be connected to the positive power supplywhile the grid 22 would become the negative grid and, therefore,connected to the negative power supply.

Further, in each of the above instances the potential required to powerthe second grid or the grid through which the air stream last flowsprior to passing into the area is surprisingly reduced from what wouldbe expected to maintain the desired atmospheric condition.

As best seen in FIG. 2, each of the grids 20 and 22 preferably includesa pair of L-shaped aluminum bars 24 and 26. Each of these bars ismounted to respective opposing surfaces of the duct, which typically ismetal, by three conventional insulator posts. Duct 30 is typicallysquare in cross section and 3 by 3 feet in dimension, but may be of anysize or shape. Bar 26 is mounted on duct 30 by insulator posts 32, 34and 36, while L-shaped bar 24 is mounted by two insulator posts 38 and40. An insulating bar 42 which is preferably of plastic material isfixedly connected to L-shaped bar 26 with a plurality of electricalfasteners attached to plastic bar 42 along its length. Similarly,aluminum bar 24 has a plurality of electrical fasteners disposed alongits length. As can be seen best in FIG. 3, each of these electricalfasteners can simply comprise a screw 44 with a pair of washers 46 and48, mounted thereon, so that a wire can be looped about screw 44,between washers 46 and 48.

Wire 50 is preferably wound in place between bars 24 and 42 as a singleunbroken wire and the portions extending between the fasteners of bar 42then removed in order to prevent a short circuit should the wire 50 bebroken at any portion thereof and fall directly onto the bottom of duct30.

Upper bar 24 is preferably connected as can be seen best in FIG. 3 to ahigh voltage source by terminals 54 and 56. As indicated, grid 20 isconnected preferably to a negative voltage source while grid 22 isconnected to a positive high voltage source.

Reference is now made to FIG. 4, which illustrates a detailed circuitschematic for applying the correct positive and negative voltages togrids 20 and 22. Sensor 100 provides an electrical output signal whichvaries as a function of the magnitude and polarity of the electricalfield in the area that is to be kept neutral or any desired charge leveleither positive or negative. This sensor is preferably the typedescribed in the above-mentioned patent to Huber, Ser. No. 384,229,filed July 31, 1973. This particular sensor provides an output signalwhich varies between 0 and 1 volt D.C., with a 0.5 volt representing aneutral environmental condition while the range 0 to 0.5 represents apositive electrical field and the range 0.5 to 1 represents a negativeelectrical field. If desired, the meter scale can be changed, forexample, to be between -5 volts and +5 volts with the neutral conditionbeing at ground. In any instance, with respect to that particular sensorand its output between 0 and 1 volts, the signal is supplied to aconventional operational amplifier 102 which amplifies the output ofsensor 100, for example by 10. Similarly, the output of sensor 100 isapplied to a second operational amplifier 104 which provides a similarlyamplified but invented output.

The output of amplifier 102 is applied to the base of transistor 106 viaconventional potentiometer 108 which can be varied to adjust thesensitivity and operation of the control circuitry. The collector oftransistor 106 is connected to a conventional full-wave rectifiercircuit 112 which is comprised of diodes 114, 116, 118 and 120. Inparticular, the collector of transistor 106 is connected to theintersection of diodes 118 and 120 which diodes each comprise a branchof the full-wave rectifier circuit 112. The connection between diodes114 and 116 similarly is connected to ground as is the emitter oftransistor 106. A conventional positive high voltage supply 130 isprovided with two input terminals 132 and 134. One of these terminals isconnected directly between the connection of diodes 114 and 120, whilethe other input terminal is connected via winding 136 to the connectionbetween diodes 116 and 118. Winding 136, together with winding 138comprises a transformer with a conventional A.C. signal applied towinding 138, for example at 115 volts, 60 Hertz.

When transistor 106 is in its non-conductive condition, no current canflow through the full-wave bridge circuit 112, and accordingly, theoutput of the high voltage supply 130, which is connected to thenegative grid via a conventional adjustment potentiometer 150 producesno voltage so that the grid in turn does not produce any ions. However,when the signal from sensor 100 is in a range indicating the need forproduction of positive ions according to the adjustment of potentiometer108, transistor 106 is driven positive so that current flows throughthat transistor to ground, the amount of current being related to thelevel of conduction of transistor 106, and the positive high voltagesupply 130 produces an output voltage having a magnitude related to theinput signal, so that positive ions are produced by positive grid 22mounted in air conditioning duct 30.

Similarly, the invented output of amplifier 104, inverted by transistor160 is supplied to the base of a further transistor 162 with themagnitude thereof being adjusted by conventional potentiometer 164.Transistor 162, like transistor 106, is connected between two branchesof a conventional full-wave rectifier 168 comprising diodes 170, 172,174 and 176. In particular, the collector of transistor 162 is connectedbetween diodes 172 and 174 with the connection between diodes 168 and176 being connected to ground. A negative high voltage supply 180 whichis identical to the positive high voltage supply 130, except as to thepolarity of its output is similarly connected to full-wave rectifier 168via coil 182 of transformer 184. Transformer 184 similarly has a secondcoil 186 to which an alternating current voltage, for example 115 volts,60 Hertz, is applied. The output of the negative high voltage signal issimilarly applied to grid 20 via potentiometer 200.

Whenever sensor 100 detects a deviation from a neutral condition, asignal is produced which, amplified by amplifiers 102 and 104, causestransistors 106 and 162 to be shifted into their conductive states andpositive and negative voltages both to be simultaneously applied togrids 20 and 22.

The following chart sets forth detected voltages and amperages forpositive and negative grids as described above in an air conditioningsystem for keeping an area neutral which was generally negative.

    ______________________________________                                        Negative Grid Positive Grid                                                   Inches                                                                              μA   KV      Inches                                                                              μA KV    Efficiency                            ______________________________________                                         6    165     13.5     6    125   11.5  76%                                   12     90     15.0    12    75    13    94%                                   18    110     15.0    18    40    8-12  36%                                   24    125     14.0    24    25    8-12  20%                                   ______________________________________                                    

Many changes and modifications can, of course, be carried out withoutdeparting from the scope of the invention. Accordingly, that scope isintended to be limited only by the scope of the appended claims.

What is claimed is:
 1. A system for maintaining a predeterminedelectrical atmosphere in an area into which air is at least periodicallypumped comprising:a first electrical grid, a second electrical grid,means for mounting said first and second grids in spaced apart relationat a location wherein the air pumped into said area passes through eachof said grids sequentially and is charged electrically as a function ofthe amplitude and polarity of the voltage on said first and second gridsrespectively, sensor means for detecting the magnitude and polarity ofthe electric field within said area and producing a control signalvarying as a function of the detected magnitude and polarity, andcircuit means connected to said sensor means for receiving said controlsignal and applying voltages to said first and second gridsrespectively, the voltage applied to one of said grids being negativeand the voltage applied to the other grid being positive, said circuitmeans varying the applied voltages so as to alter the detected field toa predetermined condition by producing in the air passing through saidgrids a net number of ions of a polarity required to produce saidpredetermined condition in said area, said circuit means furtherapplying voltages of opposite polarity respectively to said first andsecond grids simultaneously for at least a certain range of detectedelectric field magnitude.
 2. A system as in claim 1 wherein theseparation between said first and second grids is between 6 and 18inches.
 3. A system as in claim 2 wherein said separation is roughly 12inches.
 4. A system as in claim 1 wherein each said grid is comprised ofa plurality of fine wires and a frame means for fixing said wires toextend across said location.
 5. A system as in claim 4 wherein theseparation between said wires is roughly 3 inches.
 6. A system as inclaim 4 wherein said wires extend in parallel relation.
 7. A system asin claim 4 wherein said frame means includes a metal bar, means couplinga source of D.C. voltage to said bar, an insulator bar extending inparallel relation to said metal bar, a plurality of spaced fastenermeans extending along the length of said bars for fixing wire betweenthe fasteners on said metal bar and the fasteners on said insulator bar,and insulator means for mounting said bars in the upper and lowerportions of an air conditioner duct.
 8. A system as in claim 7 whereinsaid metal bar is an L-shaped aluminum bar and including a furtherL-shaped aluminum bar connected between said insulator bar and saidinsulator means.
 9. A system as in claim 8 wherein said insulator bar isplastic.
 10. A system as in claim 1 further including an airconditioning duct with said grids mounted within said duct so that airpasses through the negative grid before it passes through the positivegrid, and said sensor means mounted outside said duct.
 11. A system asin claim 1 wherein said circuit means includes:a full wave bridgerectifier having four branches, a power supply for receiving a rectifiedsignal at input terminals and providing a D.C. high voltage output, atransformer having a first winding connected to a source of alternatingvoltage and a second winding connected between one of said inputterminals and the connection between first and second of said branches,the other input terminal of said power supply being connected to theconnection between third and fourth of said branches, and electronicswitch means having a conductive and a non-conductive condition andconnected to said detecting means for shifting between said conditionsas a function of an input signal, said switch means being connected tothe connection between said first and third branches for coupling thatconnection to ground when said switch means is in said conductivecondition, the connection between said second and fourth branches beingconnected to ground so that when said switch means is in itsnon-conductive condition no current flows through said rectifier andaccordingly through said power supply, and when said switch means in itsconductive condition current flows through said switch means andaccordingly through said power supply.
 12. A circuit as in claim 11wherein said switch means has a resistance which varies as a function ofsaid input signal so that the output voltage provided by said powersupply varies in amplitude as a function of said input signal.
 13. Acircuit as in claim 12 wherein said switch means is a transistor.
 14. Acircuit as in claim 13 wherein said rectifier includes a diode in eachof said branches.
 15. A circuit as in claim 14 further including meansfor producing said input signal comprising:means for amplifying saidcontrol signal, variable resistor means connected to said amplifyingmeans, and means connecting said variable resistor means to the base ofsaid transistor.
 16. A method of maintaining an electrically neutralatmosphere in an area into which air is at least periodically pumpedcomprising the steps of:detecting the magnitude and polarity of theelectrical field within said area and producing an electrical controlsignal varying as a function of the detected magnitude and polarity and,applying a positive high voltage signal to a first electrical grid and anegative high voltage signal to a second electrical grid mounted inspaced apart relation with respect to said first grid so that the airpumped into said area passes through each of the grids sequentially andis charged electrically as a function of the polarity and magnitude ofthe voltage on the first and second grids, the applied voltages being ofsuch polarity and magnitude so as to reduce the magnitude of thedetected electrical field and thus produce said neutral atmosphere. 17.A method as in claim 16 including the further step of spacing said gridsbetween 6 and 18 inches apart.
 18. A method as in claim 17 wherein thegrids are spaced roughly 12 inches.
 19. A method as in claim 16including the further step of disposing a sensor for detecting themagnitude and polarity of the electric field within said area to producesaid control signal and disposing said grids in an air conditioning ductsupplying air to said area.
 20. A method as in claim 16 includingdisposing said first and second grids so that air passes through saidsecond grid before passing through said first grid.